From: Peter Marshall (petermarshall@cix.co.uk)
Date: 02/24/02-05:15:21 AM Z
> > I think the Southeby item must be a photo-copy of an existing
> > picture. Arthur
>
>
> Exactly Arthur. I went to Sotheby's last Saturday and spoke to the
> director of the show after trying to figure out what it was as there
> was no explanation beside the piece and the catalogue gave elusive
> description.
>
> An engraving was laid against a wet light sensitive piece of paper.
> That piece of paper was then "developed" so that the relief remained.
> That in turn was pressed into a second plate.
> That plate then could make "indefinite number of prints" or facsimiles
> was the word he used. The image for sale is the only "print" known from
> that plate.
>
> Yes, it is of a horse being pulled by a boy. It does not in any way
> look like a "photograph" as in something documented with a camera/lens.
>
> IMHO I would say it was, at best, a contact print of an engraving. In
> that sense, I guess it could be called a photograph. It was not the
> original visual recording of something occurring.
>
> Carole
Carole,
I think this mainly demonstrates that Sotheby's are auctioneers and not
photo-historians. Though they do have people working for them who know
their stuff, clearly you were not speaking to one of them.
What he told you was vaguely correct. I think that the engraving was oiled
to make it more transparent, then placed in contact with a copper sheet
coated with bitumen (or similar material), and exposed for several hours
or days. Light hardens the bitumen in the exposed areas. The plate was
then washed in a solvent which removed the unhardened bitumen,
corresponding to the black lines in the original etching.
The plate was then etched, probably using ferric chloride, when the
remaining hardened bitumen acted as a resist, leaving the areas covered by
it unaffected. The plate could then be cleaned off, inked and printed
using an etching press.
The ink would be held in what were the unexposed areas of the plate,
corresponding to the black lines of the original etching, thus giving a
positive working process
I'm not sure these details are entirely correct, as I've not worked with
the original material from Niepce's papers, but, like others on this list,
I have made pictures by a similar photo-etching method, as well as by a
later improvement of it.
Peter Marshall
Photography Guide at About http://photography.about.com/
email: photography.guide@about.com
_________________________________________________________________
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and elsewhere......
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